Structural health monitoring of grouted connections for offshore wind turbines by means of acoustic emission: An experimental study

Grouted connections for offshore wind turbines are formed by attaching overlapping steel piles with an ultra-high strength cementitious grout. The structural performance of grouted connections is critical for the substructures in order to exhibit sufficient resistance to environmental loads. The long-term integrity of the grout core can be compromised due to the complex stress states present, leading to unexpected slippage and gaps in the steel-grout interface, grout cracking and water ingress. This paper presents the results of an experimental investigation on damage evolution and failure mechanisms occurring within grouted connections in laboratory-based bending tests using acoustic emission. A parametric analysis of the detected acoustic emission signals has been conducted. The acoustic emission activity has been correlated with load-displacement measurements and the observed specimen failure modes. For the tested grouted connections, the number of acoustic emission hits and the signal duration were employed to identify damage evolution during load application. Root mean square and the ratio of rise time to amplitude were found to be useful Key Performance Indicators (KPIs) for damage prognosis. Finally, an improved b-value analysis has been performed, and the computed drops were well-associated with grout cracking within the connection.